<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h2>词法作用域</h2>
</body>
<script>
    let username='jack'

    function fn2() {
        console.log('我打印多少：',username)
    }

    function fn1() {
        var username='alice'
        fn2()
    }

    fn1()  //?alice,
</script>
</html>